1. Field of the Invention
The present invention relates to methods and apparatus for separation of solids from liquids and separation of liquids from liquids (such as oil from water) by dissolved gas floatation. The methods and apparatus of the present invention are particularly suitable for supplying dissolved air and mixing of chemicals for use in separation of solids in dissolved air floatation clarifiers.
2. Description of Related Art
The methods and apparatus for mixing fluids and dissolving gases in liquids disclosed in co-pending patent application Ser. No. 09/879,496, filed Jun. 12, 2001, now U.S. Pat. No. 6,669,843, in the name of Johnny Arnaud and assigned to the same assignee as the present application where liquids can be totally saturated with dissolved gases at any pressure, also provides the opportunity for improvements in the methods and apparatus for separation of both solids and trace organic fluids suspended in a second fluid, such as water, by dissolved gas floatation.
Saturating a liquid such as water with a dissolved gas under pressure then injecting the saturated liquid into other water contaminated with suspended solids or suspended liquids, such as oil, and releasing the pressure allows the gas to come out of solution as microscopic (small) bubbles that rise slowly in the liquid. As the bubbles form they attach themselves to the contaminating suspended solid particles and liquid droplets increasing the buoyancy and accelerating the rise of the particles and droplets to the surface where they can be removed. The process can be used for separating solids and trace organic contaminants from fluids in dissolve air floatation clarifiers. While that exemplary application is described in the present invention, it is understood that there are many other implementations without deviating from the intent and spirit of the present invention.
The basic requirements of a system used for gas floatation of both solids and liquids have been well defined to include introduction of finely dispersed gas bubbles into the stream to be treated, a floatation zone of minimum turbulence, and a means of removing the floated material. The microscopic bubbles are obtained by either a recycle pressure system where a portion of the clarified water is recycled through a dissolved gas generator and then mixing the saturated water with the incoming wastewater stream as it enters the clarifier, or by a full-stream pressure system where the entire incoming wastewater stream flows through a dissolved gas generator ahead of the clarifier. In addition, chemicals to aid in separation of the contaminants from the water are commonly introduced into the stream and have become part of the basic requirements of gas floatation systems. The selection of systems and methods for treating specific wastewater streams depends on what contaminants are present, whether the contaminants are predominantly suspended solids with a small amount of liquid contaminants or predominantly liquids with a small amount of suspended solids, and what is to be done with the contaminants removed from the treated water.
In treating water for removal of contaminants, various chemicals perform selected functions in the treating process. The use of chemicals in wastewater treatment is discussed in U.S. Pat. No. 6,254,267, dated Jul. 3, 2001, in the name of Johnny Arnaud and assigned to the same assignee as the present application, incorporated by reference herein in its entirety. The discussions in that referenced patent on use of chemicals in wastewater treatment are repeated for clarity. The chemicals can be liquids or solids in granular or powder form. Some solids are dissolved into and used as liquids in the treating process. Other chemicals may perform their treating functions as solids.
Many solid-liquid separation processes in wastewater treatment employ coagulation and flocculation. Laymen have long used the terms “coagulation” and “flocculation” interchangeably in discussing solid-liquid separation processes. Colloid scientists, however, have adopted a more specific usage. “Coagulation” implies aggregation caused by compression of the electrical double layers surrounding colloidal particles. “Flocculation” is restricted to cases where polymer bridging or some similar mechanism operates. Coagulation and flocculation are essential in many solid-liquid separation processes, since many suspended particles are too small for gravitational settling alone to effectively remove the particles. Coagulants can be purchased in both the liquid and solid phases. Polymers used as flocculating agents can also be obtained in liquid and solid phases. In liquid phase, those chemicals must be mixed and dispersed to react with the contaminants throughout the water. In powdered or granulated solid form, those chemicals must be dissolved first and then mixed with water in order to react with the contaminants.
Chemicals that remain powdered during the treating process may also be used in addition to coagulants and flocculants to remove contaminants from water. Bentonite clays and activated carbon powders exemplify such solid chemicals used to remove organic and dissolved metal contaminants from water. The powders must be wetted, fed into the water, and dispersed in order to reach the contaminants throughout the body of water to be treated. Once injected into the water, the powders may also have to be coagulated and flocculated so they can be separated by floatation or settling to remove them from the water.
Most of the deficiencies of the present dissolved gas floatation systems are in the quality of the bubbles produced, size and cost of the apparatus used to generate the bubbles, method of introducing the bubbles into the stream of water to be treated, and the success of mixing and dispersing the chemicals added by the existing apparatus used.
The dynamics of fluid flow generally can be expressed by conservation of energy, momentum, and impulse.